Hypereutectic aluminum alloys containing, by weight, from 14 to 25% silicon have been widely used in sliding parts as die casting alloys having excellent abrasion resistance. Especially, 390 Alloy comprising by weight 16.0 to 18.0% Silicon(Si), 4.0 to 5.0% Copper(Cu), 0.45 to 0.65% Magnesium(Mg), 0.1% or less Zinc(Zn), 0.6 to 1.1% Iron(Fe), 0.1% or less Manganese(Mn), 0.02% or less Titanium(Ti), trace of Phosphorous(P), and the remainder being Aluminum(Al), is so highly resistant against abrasion that it is used as an aluminum engine block free from cast iron liners. The alloy disclosed in JP-B-No. 53-37810 (the term "JP-B" as used herein means an "examined Japanese patent publication") comprising by weight, 13.5 to 16.0% Si, 4.0 to 5.0% Cu, 0.5% or less Mg, 1.0% or less Zn, 1.3% or less Fe, 0.5% or less Mn, 0.05 to 0.1% P, 0.5% or less Nickel(Ni), 0.3% or less Tin(Sn), and the remainder being Al, is 390-Alloy based, in which the alloy's machinability is improved without considerably damaging its original abrasion resistance. The alloy is used in a broad field as housings of door closers, etc.
The alloy disclosed in JP-A-No. 60-2643 (the term "JP-A" as used herein means a published unexamined Japanese patent application) containing by weight, 5.0 to 22.5% Si, 5.5 to 10.5% Cu, 0.8 to 1.5% Fe, 0.85 to 1.5% Mg, 0.002 to 0.025% P, and the remainder being Al and inevitable impurities, is an aluminum alloy for die castings suitably used for sliding parts which work satisfactorily when used with either high- or low-viscosity lubricating oils.
The excellent abrasion resistances of the aforesaid 390 Alloy and the alloy disclosed in JP-B-No. 53-37810 have been attained by existing primary Si crystals. Therefore, an amount of Si is necessarily increased to improve abrasion resistance. Increasing the concentration of Si to 20 wt % or more, however, leads to higher casting temperature and brings about disadvantages such as shortening the mold life. Furthermore, increasing primary Si crystals leads to a lowering of machinability. It is therefore preferable to improve abrasion resistance without adding a large amount of Si.